1. Field of the Invention
The present invention relates to a powder conveyance device capable of conveying powder, such as toner, etc., from a powder container section to a conveyance destination located downstream of the powder container section via a powder conveyance pipe, an image forming apparatus including the powder conveyance device, and a process cartridge.
2. Discussion of the Background Art
Conventionally, an image forming apparatus, such as a copier, a facsimile, a printer, etc., equipped with a toner conveyance device has been known.
As shown in FIG. 19, the Japanese Patent Application Laid Open No. 2005-024665 describes a toner conveyance device that employs a toner conveyance pipe for guiding toner from a toner container section that stores the toner to a developing device provided below the toner container section. The toner conveyance pipe 143 includes a upstream side horizontal section 143a communicating with the toner container section 147 while substantially extending horizontally, a slant section 143c largely inclining downward a developing device 155 on the downstream side of the upstream side horizontal section 143a, and a downstream side horizontal section 143e substantially extending horizontally while communicating with a developing device 155 at the downstream side of the slant section 143c. A conveyance coil 170 is provided in the toner conveyance pipe 143 to stir and convey the toner.
The toner installed in the toner container section 147 is conveyed to the upstream side horizontal section 143a by the conveyance coil 170. When the toner conveyed to the upstream side horizontal section 143a is further conveyed to the slant section 143c by the conveyance coil 170, the toner drops down to the downstream side horizontal section 143e at once from the slant section 143c by its own weight in addition to a conveyance force provided by the conveyance coil 170. In this way, the toner conveyed to the downstream side horizontal section 143e is further conveyed by the conveyance coil 170 to a replenishment inlet 145 communicating with the developing device 155, whereby the toner is ejected to the developing device 155.
Since the toner drops down at the slant section 143c to the downstream side horizontal section 143e at once by its own weight in addition to the conveyance force from the conveyance coil 170, the toner scarcely accumulate thereon and most part of the space in the pipe of the slant section 143c is occupied by air. The toner is blended with air by the conveyance coil 170 or the like in the toner conveyance pipe 143. Especially, at the slant section 143c where the inside of the pipe space is almost occupied by the air, the toner tends to be blended with the air more than the other section. As a matter of fact, the higher the rate at which the toner is blended with air, the higher the toner fluidity is.
Thus, at the slant section 143c where the toner is readily blended with air, the toner is excessively blended therewith, whereby the fluidity of the toner excessively increases. When the fluidity of the toner excessively increases, the toner behaves like liquid, and ends up flowing from the slant section 143c to the developing device 155 at once via the replenishment inlet 145 without conveyance of the conveyance coil 170 due to a dropping force caused when dropping down the slant section 143c. 
In this way, when the toner flows at once from the replenishment inlet 145 into the developing device 155 regardless of the conveyance of the conveyance coil 170, toner replenishment to the developing device 155 results in unstable.